Aircraft typically include a variety of movable aerodynamic devices for directional control of the aircraft and for altering the lift characteristics of the aircraft. For example, fixed wing aircraft typically includes slats and flaps mounted to the leading and trailing edges of the wings. Certain aircraft may include Krueger flaps mounted to the inboard section of the wings on the leading edge and slats mounted to the outboard section of the wings on the leading edge. Krueger flaps and slats may be deployed from the leading edge of the wings during certain phases of flight in order to increase effective wing camber and maintain airflow over the wings at high angles of attack.
Flaps may also be mounted to the trailing edges of the wings in order to increase the lift generated by the wings when the aircraft is moving at relatively low airspeeds. For example, trailing edge flaps may be deployed generally downwardly during takeoff to increase lift and may then be retracted during the cruise portion of the flight. The trailing edge flaps may again be deployed during the approach and landing phases of the flight in order to increase lift by increasing effective wing camber and wing area to compensate for the lower airspeed of the aircraft.
In addition, certain aircraft may include Gurney flaps which may be mounted to the wings to improve lift. Gurney flaps may be configured as small spanwise protrusions which may be deployable generally perpendicularly from the wing trailing edge on the underside of the wings to increase the wing lift coefficient when the aircraft is moving at relatively high airspeeds such as during cruise flight. Gurney flaps may increase the wing lift coefficient without significantly increasing drag by extending no further than the boundary layer of airflow passing over the wings. Gurney flaps may maintain attachment of the airflow over the wing surface and thereby improve the aerodynamic efficiency of the wings which may reduce fuel consumption.
Aerodynamic devices such as the above-mentioned flaps and slats are required by the Federal Aviation Administration (FAA) to include a locking mechanism for maintaining the device in the selected deployed position without intervention by the pilot. FAA regulations additionally allow for automatic retraction of aerodynamic devices from the deployed position in certain circumstances. For example, aerodynamic devices may be automatically retracted upon the aircraft encountering wind shear to avoid overloading the wing structure. For an aircraft fitted with Gurney flaps and moving at 500 to 600 miles per hour typical of cruise flight, it may be necessary to retract or release the Gurney flaps in a relatively short period of time (e.g., less than 300 milliseconds) to prevent overloading the wing.
The prior art includes several actuators such as hydraulic and electro-mechanical actuators for deploying and retracting aerodynamic devices. Although generally effective for their intended purpose, hydraulic and electro-mechanical actuators may have a relatively low specific holding torque for maintaining an aerodynamic device in a deployed position and therefore must be relatively large in physical size to generate sufficient holding torque to lock the aerodynamic device in the deployed position. Unfortunately, the relatively large physical size of prior art actuators presents challenges in integrating the actuator into the narrow confines of the wing trailing edge. In addition, the relatively large physical size of such actuators increases weight, complexity and cost of the aircraft. Furthermore, such prior art actuators may lack the ability to retract or release an aerodynamic device such as a Gurney flap from its deployed position in an extremely short period of time upon encountering wind shear for an aircraft moving at relatively high airspeeds.
As can be seen, there exists a need in the art for an actuator which is of relatively small size and which can generate a relatively large amount of holding torque for maintaining a deployable device in a deployed position. Furthermore, there exists a need in the art for an actuator capable of retracting or releasing a deployed device in a relatively short period of time on the order of milliseconds.